What about seatbelts. Must they be used?
Again seatbelts are covered by the driving regulations of the country you are driving in. In the UK, they are covered by http://www.dvla.gov.uk/ or http://www.direct.gov.uk/en/TravelAndTransport/Highwaycode/index.htm?cids=Google_PPC&cre=Highway_Code
If they are fitted in a motorhome, then they must be used by the driver and passengers while the vehicle is being driven.
